Earlier devices of this same general character have been employed but because of certain limitations in their construction and operation they have not been too successful. In such devices a drum or barrel-shaped hollow body wholly enclosed all of the vanes and their side supports therewithin, with the result that not only did these interior parts of the device interfere with and obstruct the flow of air through the hollow-shaped barrel or drum but the disposition of the vanes within the barrel member required dismantling of the device to adjust the vanes, assuming such adjustability was built into the device. As a result of such designs, these earlier air-flow devices were inefficient, lacking convenient adjustment on the one hand for attaining the desired air diffusion and having interior obstructions to air flow which interfered with the volume and throw of the discharged air.